/*
 * Copyright 2021 ZhongChao Blockchain Technology Research Institute.
 *
 * Copyright ConsenSys AG.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 *
 * This file has been modified by ZhongChao Blockchain Technology Research Institute to add support for Brochain.
 *
 * SPDX-License-Identifier: Apache-2.0
 */
package link.luyu.plugin.brochain.trie;

import java.util.List;
import java.util.Optional;
import java.util.function.Function;
import org.apache.tuweni.bytes.Bytes;
import org.apache.tuweni.bytes.Bytes32;

public class RestoreVisitor<V> implements PathNodeVisitor<V> {

    private final NodeFactory<V> nodeFactory;
    private final V value;
    private final NodeVisitor<V> persistVisitor;

    public RestoreVisitor(
            final Function<V, Bytes> valueSerializer,
            final V value,
            final NodeVisitor<V> persistVisitor) {
        this.nodeFactory = new DefaultNodeFactory<>(valueSerializer);
        this.value = value;
        this.persistVisitor = persistVisitor;
    }

    @Override
    public Node<V> visit(final ExtensionNode<V> extensionNode, final Bytes path) {
        final Bytes extensionPath = extensionNode.getPath();

        final int commonPathLength = extensionPath.commonPrefixLength(path);
        assert commonPathLength < path.size()
                : "Visiting path doesn't end with a non-matching terminator";

        if (commonPathLength == extensionPath.size()) {
            final Node<V> newChild =
                    extensionNode.getChild().accept(this, path.slice(commonPathLength));
            return extensionNode.replaceChild(newChild);
        }

        // path diverges before the end of the extension - create a new branch

        final byte leafIndex = path.get(commonPathLength);
        final Bytes leafPath = path.slice(commonPathLength + 1);

        final byte extensionIndex = extensionPath.get(commonPathLength);
        final Node<V> updatedExtension =
                extensionNode.replacePath(extensionPath.slice(commonPathLength + 1));
        final Node<V> leaf = nodeFactory.createLeaf(leafPath, value);
        final Node<V> branch =
                nodeFactory.createBranch(leafIndex, leaf, extensionIndex, updatedExtension);

        if (commonPathLength > 0) {
            return nodeFactory.createExtension(extensionPath.slice(0, commonPathLength), branch);
        } else {
            return branch;
        }
    }

    @Override
    public Node<V> visit(final BranchNode<V> branchNode, final Bytes path) {
        assert path.size() > 0 : "Visiting path doesn't end with a non-matching terminator";
        BranchNode<V> workingNode = branchNode;

        final byte childIndex = path.get(0);
        if (childIndex == CompactEncoding.LEAF_TERMINATOR) {
            return workingNode.replaceValue(value);
        }

        for (byte i = 0; i < childIndex; i++) {
            workingNode = persistNode(workingNode, i);
        }

        final Node<V> updatedChild = workingNode.child(childIndex).accept(this, path.slice(1));
        return workingNode.replaceChild(childIndex, updatedChild);
    }

    private BranchNode<V> persistNode(final BranchNode<V> parent, final byte index) {
        final Node<V> child = parent.getChildren().get(index);
        if (!(child instanceof StoredNode)) {
            child.accept(persistVisitor);
            final PersistedNode<V> persistedNode =
                    new PersistedNode<>(null, child.getHash(), child.getRlpRef());
            return (BranchNode<V>) parent.replaceChild(index, persistedNode);
        } else {
            return parent;
        }
    }

    @Override
    public Node<V> visit(final LeafNode<V> leafNode, final Bytes path) {
        final Bytes leafPath = leafNode.getPath();
        final int commonPathLength = leafPath.commonPrefixLength(path);

        // Check if the current leaf node should be replaced
        if (commonPathLength == leafPath.size() && commonPathLength == path.size()) {
            return nodeFactory.createLeaf(leafPath, value);
        }

        assert commonPathLength < leafPath.size() && commonPathLength < path.size()
                : "Should not have consumed non-matching terminator";

        // The current leaf path must be split to accommodate the new value.

        final byte newLeafIndex = path.get(commonPathLength);
        final Bytes newLeafPath = path.slice(commonPathLength + 1);

        final byte updatedLeafIndex = leafPath.get(commonPathLength);

        final Node<V> updatedLeaf = leafNode.replacePath(leafPath.slice(commonPathLength + 1));
        final Node<V> leaf = nodeFactory.createLeaf(newLeafPath, value);
        final Node<V> branch =
                nodeFactory.createBranch(updatedLeafIndex, updatedLeaf, newLeafIndex, leaf);
        if (commonPathLength > 0) {
            return nodeFactory.createExtension(leafPath.slice(0, commonPathLength), branch);
        } else {
            return branch;
        }
    }

    @Override
    public Node<V> visit(final NullNode<V> nullNode, final Bytes path) {
        return nodeFactory.createLeaf(path, value);
    }

    static class PersistedNode<V> implements Node<V> {
        private final Bytes path;
        private final Bytes32 hash;
        private final Bytes refRlp;

        PersistedNode(final Bytes path, final Bytes32 hash, final Bytes refRlp) {
            this.path = path;
            this.hash = hash;
            this.refRlp = refRlp;
        }

        /** @return True if the node needs to be persisted. */
        @Override
        public boolean isDirty() {
            return false;
        }

        /** Marks the node as being modified (needs to be persisted); */
        @Override
        public void markDirty() {
            throw new UnsupportedOperationException(
                    "A persisted node cannot ever be dirty since it's loaded from storage");
        }

        @Override
        public Node<V> accept(final PathNodeVisitor<V> visitor, final Bytes path) {
            // do nothing
            return this;
        }

        @Override
        public void accept(final NodeVisitor<V> visitor) {
            // do nothing
        }

        @Override
        public void accept(final Bytes location, final LocationNodeVisitor<V> visitor) {
            // do nothing
        }

        @Override
        public Bytes getPath() {
            return path;
        }

        @Override
        public Optional<V> getValue() {
            throw new UnsupportedOperationException(
                    "A persisted node cannot have a value, as it's already been restored.");
        }

        @Override
        public List<Node<V>> getChildren() {
            // return List.of();
            return java.util.Arrays.asList(); // dx: java8
        }

        @Override
        public Bytes getRlp() {
            throw new UnsupportedOperationException(
                    "A persisted node cannot have rlp, as it's already been restored.");
        }

        @Override
        public Bytes getRlpRef() {
            return refRlp;
        }

        @Override
        public boolean isReferencedByHash() {
            // Persisted nodes represent only nodes that are referenced by hash
            return true;
        }

        @Override
        public Bytes32 getHash() {
            return hash;
        }

        @Override
        public Node<V> replacePath(final Bytes path) {
            throw new UnsupportedOperationException(
                    "A persisted node cannot be replaced, as it's already been restored.");
        }

        @Override
        public void unload() {
            throw new UnsupportedOperationException(
                    "A persisted node cannot be unloaded, as it's already been restored.");
        }

        @Override
        public String print() {
            return "PersistedNode:" + "\n\tPath: " + getPath() + "\n\tHash: " + getHash();
        }
    }
}
